Ball screws are in common use today for a variety of applications. One such application is to control the displacement of an airfoil surface, such as a trim tab. In such application, a drive mechanism is mounted on the aircraft, and is used to selectively rotate a ball screw in the appropriate angular direction. A nut is threadedly mounted on the ball screw, and is arranged to engage the airfoil surface at an eccentric location. Thus, the motor may selectively rotate the ball screw relative to a nut in one angular direction to cause the airfoil surface to move or pivot in one direction, and may selectively rotate the ball screw in the opposite angular direction relative to the nut to cause the airfoil surface to move or pivot in the opposite direction.
No-back devices are used with such mechanisms to provide a force that resists rotation of the ball screw in a direction that would result in movement of the airfoil surface in the direction of the applied aerodynamic force (i.e., an “aiding” load), while applying little or no force resisting rotation of the ball screw in the direction that would result in movement of the airfoil surface against the applied aerodynamic force (i.e., an “opposing” load). As used herein, a ball screw refers to the screw and the nut threaded thereon. The screw may be rotated relative to the nut, or the nut may be rotated relative to the screw, as desired.
One example of such a no-back device is shown and described in U.S. Pat. No. 6,109,415, the aggregate disclosure of which is hereby incorporated by reference.
Such aircraft applications typically require that the airfoil surface be placed in a slip stream before an “aiding” or “opposing” load may be applied to the ball screw.
It would be generally desirable to be able to check the apparent operational integrity of such a no-back device while the aircraft is on the ground and while the airfoil surface is unloaded.
Details of other no-back devices are shown and described in U.S. Pat. Nos. 6,631,791 B2 and 7,672,540 B1, the aggregate disclosures of which are hereby incorporated by reference.